APPENDIX E. — PALEONTOLOGY. 413 



Allorisma tebminalis, Hall, (n. sp.) 



Plate IV. Fig. 4 a b. 



Shell elongate-ovoid, with the posterior extremity extended and 

 sub-acute ; beaks anterior, or in a line with the anterior extremity 

 of the shell ; surface marked by strong concentric ridges, which, 

 diverging from the beak, are more prominent on the central portion 

 of the shell, and gradually die out on the cardinal line. The shell 

 is also quite smooth toward the basal margin, with the exception 

 of the rather coarse concentric strise which cover the entire surface. 



Fig. 4 a, view of the left valve. 



Fig. 4 b, anterior view of the shell. 



Loc. from the Big Blue River. 



Nucula arata. Hall, (n. sp.) 



Plate IV. Fig. 5 a b. 



Shell oval-ovate, rounded before, and gradually narrowing be- 

 hind the beaks (posterior extremity broken off) ; beaks prominent, 

 closely incurved ; posterior lunule elongated and distinctly de- 

 fined; surface marked by distinct (rather sharp where unworn) 

 equal concentric ridges, scarcely so wide as the furrows between 

 them. The ridges, when seen in a longitudinal direction, have an 

 imbricated appearance. 



Fig. 5 a, the right valve, showing the anterior extremity broken 

 off. 



Fig. 5 b, a cardinal view, showing the beaks and defined pos- 

 terior lunule. 



This beautiful species occurs with Terehratula, Spirifer, and 

 Productus, in a decomposing limestone, on the east side of the 

 Missouri River, below Weston. 



GASTEROPODA. 



Pleurotomaria coronula, Hall, (n. sp.) 



Plate IV. Fig. 6 a b c d. 



Depressed trochiform, volutions about five, angular, slightly 

 convex on the upper side, and sloping almost uniformly from the 

 suture to the margin ; lower surface more rounded ; aperture sub- 

 quadrangular ; strise bent abruptly backward on the acute outer 



